Amoeba (redirected from amebas)

amoeba: see ameba.

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amoeba

Amoeba (magnified).

(credit: Russ Kinne/Photo Researchers)

One-celled protozoan that can form temporary extensions of cytoplasm (pseudopodia) in order to move about. Some amoebas are found on the bottom of freshwater streams and ponds. Others live in the human digestive system; one type causes amebic dysentery in humans. Each amoeba contains a small mass of jellylike cytoplasm with vacuoles and a nucleus. Food is taken in and material is excreted at any point on the cell surface. Amoebas are used extensively in cell research for determining the relative functions and interactions of the nucleus and the cytoplasm.

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amoeba (US), ameba

any protozoan of the phylum Rhizopoda, esp any of the genus Amoeba, able to change shape because of the movements of cell processes (pseudopodia). They live in fresh water or soil or as parasites in man and animals

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Amoeba [ə′mē·bə]

(invertebrate zoology)

A genus of naked, rhizopod protozoans in the order Amoebida characterized by a thin pellicle and thick, irregular pseudopodia.

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1.	(operating system)	Amoeba - A distributed operating system developed by Andrew S. Tanenbaum and others of Vrije Universiteit, Amsterdam. Amoeba is only available under licence from the VUA, but is free of charge and includes all source, binaries and documentation. http://am.cs.vu.nl/.
2.	(computer, abuse)	Amoeba - A derogatory term for Commodore's Amiga personal computer.

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Amoeba 

the order of the simplest organized protozoa of the class Sarcodina. Most live in fresh waters, a few in the soil; there are parasitic forms. They are usually of microscopic dimensions up to 50 μm, but there are also “giants” such as Pelomyxa, which grows to 2–3 mm. Amoebas have no constant body shape; their cytoplasmic body forms extrusions or pseudopodia which aid in motion and food gathering. They feed on bacteria, minute algae, and protozoa. The amoeba engulfs the food particle and from its cytoplasm the amoeba secretes digestive juices and forms a food vacuole within which the food is dissolved and is incorporated into the cytoplasm. The excretion of water (osmoregulation) and metabolic products occurs through the contractory vacuoles, which gradually accumulate waste matter and discharge it at the surface.

Amoebas ordinarily have one nucleus, but Pelomyxa is multinucleate. The majority of amoebas multiply asexually, dividing in two. The division of the body is preceded by mitosis in the nucleus. A sexual process is known only in very rare cases.

Upon subjection to unfavorable conditions—for instance, insufficient food, cold, or drying of the water body—the amoeba’s body becomes round and the surface of its cytoplasm becomes a dense protective layer; a cyst forms that is resistant to unfavorable effects of the dormant stage. Freshwater amoebas can serve as a water pollution index. Parasitic amoebas live in the intestines of various animals and man. Among these the most harmful is the dysentery amoeba (Entamoeba histolytica), which produces a severe form of amoebic dysentery in man. Infection occurs via cysts, which remain viable outside the human body.

REFERENCES

Dogel’, V. A., Iu. I. Polianskii, and E. M. Kheisin. Obshchaia protozoologiia. Moscow-Leningrad, 1962.
Seravin, L. N. Dvigatel’nye sistemy prosteishikh. Leningrad, 1967.

A. A. STRELKOV